GB1468893A - Multi-probe flux leakage testing apparatus - Google Patents

Abstract

1468893 Detecting flaws magnetically MAGNETIC ANALYSIS CORP 3 June 1974 [7 June 1973] 24550/74 Heading G1N In a multi-probe flux leakage flaw testing apparatus the outputs of the probes are processed to yield bi-polar signals having positive and negative portions corresponding to the largest positive and negative portions simultaneously occurring in the probes. Testing Assembly Fig. 4 and Figs. 3, 5, 6 (not shown). The tube or rod 31 to be tested passes in the direction shown through a rotatable head 35 mounted on bearings 34 on hub 33 fixed to back plate 32, the head being driven by a belt. Mounted on the head are a pair of half cylinders 37, 37' between which two diametrically opposed adjustable pole pieces 38, 38' are clamped and which provide a steady magnetic field for passing through the tube 31. Probe carriers 44, 44' held in position in the cylinders 37, 37' by members 44 each supports a probe cartridge 45, 45' supported by spring biased lever arms 46, 46'. Each cartridge contains a desired number of probes, two as shown, of the type including a U-shaped magnetic core wound by a coil and having trapezoidal pole pieces adjacent tube 31, Fig. 2a (not shown). As the head rotates tube 31 is scanned in four helical paths. The probe circuitry, to left of dashed line of Fig. 8, is mounted on cards 51, 51' connected to slip rings 52-54 contacting brush assemblies 52'-54' to enable the signals to be passed to the processing circuitry. Circuitry Fig. 8. The probe coils 25-1, 25-2, .. 25-n are each connected via bi-polar amplifiers 61 and filter circuit 66 to respective opposite poled rectifiers 64, 65 with the diodes 64 from all the channels being connected together by line 68 and diodes 65 by line 69 yielding signals 73, 74. The circuit functions to produce on lines 68, 69 only the largest positive and negative signals simultaneously applied to respective sets of diodes and all diodes except those passing these largest signals are back biased. The signals in lines 68, 69 are then applied to transistors 75, 76 which forms a combining circuit to yield a bi-polar signal 79 at 80 which is fed via slip ring 81 to a connector 82 on the stationary mounting. In order to distinguish between outside diameter, O.D., flaws and inside diameter, I.D., flaws two channels are provided which include respective R.C. band pass filters 92, 93. After filtering at 94, 94' to eliminate high frequency transients the resultant flaw signals are supplied to vertical deflection circuits of oscilloscopes 96, 96' and to circuits 98, 98' which may include threshold circuits actuating an alarm, marker or segregator whenever either the positive or negative portions exceed a predetermined value. The head may be fixed and include a number of probes arranged in a line along tube 31, Fig. 2 (not shown). Flat plates may be tested instead of tubes or rods.